perf tools: Use getconf to determine number of online CPUs

Parsing /proc/cpuinfo is a fiddly, arch-dependent business and a recent
change to get it working for Sparc broke arm and arm64 platforms.

Use sysconf to determine the number of online CPUs only parsing
/proc/cpuinfo when sysconf is not available.

Signed-off-by: Will Deacon <will.deacon@arm.com>
Acked-by: Jiri Olsa <jolsa@kernel.org>
Tested-by: Arnaldo Carvalho de Melo <acme@redhat.com>
Cc: David Ahern <david.ahern@oracle.com>
Cc: Mark Rutland <Mark.Rutland@arm.com>
Cc: Namhyung Kim <namhyung@kernel.org>
Link: http://lkml.kernel.org/r/20150423140454.GJ1652@arm.com


[ Made it fall back to parsing /proc when getconf not found ]
Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>